Electric contacting element



Patented Nov.'2l, 1939 UNITED STATES ELECTRIC CONTACTING ELEMENT FranzR. Hensel, Indianapolis, Ind., assignor to P, It. Mallory & (30., Inc.,Indianapolis, Ind., a corporation of Delaware No Drawing.

1 Claim.

This invention relates to the production of electric contactingelements.

It is an object of this invention to provide a new contact element whichwill have a very high 5 melting point, combined with comparatively lowelectrical resistivity.

It is a further object of this invention to produce a contact materialwhich will not dissociate at operating temperatures, and thus formlayers of high contact and specific resistance.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the fea tures of construction,combinations of elements and arrangements of parts which will beexemplified in the constructions hereinafter set forth and the scope ofthe application of which will be indicated in the claim. a

In the prior art, compositions have been mentioned in which refractorymetals and their compounds were impregnated with a lower melting pointmetal of the nature of silver and copper plus gold, or iron, nickel andcobalt, or a metal of the platinum or palladium group. Usually themetals selected are molybdenum or tungsten or their carbides. The metalstungsten and molybdenum, which are highly refractory, have thedisadvantage that they oxidize at comparatively low temperature andcertain forms of tungsten and molybdenum oxides produce very highcontact resistance. As a matter of fact, they act as insulators. Thecarbides of these metals, which also have been tried, in many instances,have usually a very high specific resistance. The present inventioncontemplates electric contacting elements formed of metal compositionscomprising as'essential ingredients thereof one or more metal compoundsof metals selected from the fourth and fifth groups of the periodicsystem, namely, titanium, zirconium, hafnium, vanadium, columbium andtantalum combined with nitrogen and a low melting point metal selectedfrom the group silver, copper and gold or an alloy of such metals. Themetal compositions may also include substantial percentages of otherrefractory metals or refractory metal compounds such as metals of thetungsten group and other refractory compounds if desired.

An important advantage arising from the use of refractory nitrideslisted above resides in their Application September 29, 1937, Serial No.166,371

relatively high electrical conductivity whereby they are renderedadvantageous for electrical purposes. As an example, the electricalresistivity of two of these compounds are here listed:

. Melting point Resistivity Compoum microhms/c. m. g gs gz Zirconiumnitride 13.6 3255 Titanium nitride 21. 7 3220 It is quite remarkablethat the nitrides of such metals as zirconium, hafnium and titanium showa much lower resistivity than the elements themselves. Pure zirconium,for instance, has a resistivity of 44.6 microhms c. m., while titaniumhas a resistivity of almost microhms c. m.

Tests have shown that the carbides of the sixth group of the periodicystem, particularly the carbides of molybdenum and tungsten, are easilyattacked by the air at elevated temperatures.

The compounds of the present invention are more resistive to an attackof oxidizing atmosphere at such elevated temperatures.

Any alloy of this nature may be employed to advantage for electric usessuch aselectrical contacting elements. a

I have found that metal mixtures of the following combinations areparticularly desirable? Per cent Borides and nitrides of elementsselected from the group consisting of titanium, zirconium, hafnium,vanadium, columbium, tantalum either individually or in combination50-99 Silver, copper or gold or alloys containing said elements asprincipal ingredients 150 the impregnation process.

will nottend to stick. Sticking is usually caused by the fusing togetherof small particles of the low melting point metal. However, by selectingthe proper ratios of the refractory compounds with or without refractorymetals of the nature of tungsten and molybdenum, a structure is producedwhich will completely separate the low melting point particles, so thatin service they can not flow together if arcing occurs, and makecontacts stick.

While it was necessary previously to use low percentages of refractorycompounds in order to obtain a low specific resistance, with the newmaterials described herein, almost any percentage up to 99% of therefractory alloys may be used and still a good conductivity may beobtained without excessive over-heating.

The methods by which the above mentioned combinations are produced mayvary. I may take, for instance, the powders of the refractory metalcompounds and mix them with the powders of the metals of the tungstengroup and the powders of the low melting point alloys. After an intimatemixture has been obtained, the powders can be pressed, either cold or atelevatd temperatures. After the pressing, the powders may be sintered,either below the melting point of the low melting point metal, or above.After the sintering operation, the material may be repressed andresintered and then swaged, rolled or forged to any desired shape or itmay be used in the repressed condition.

Another possibility is to mix the powders of the refractory compoundsand the refractory metals together, with or without the addition of ametal of the iron group. After pressing and sintering, or pressing,sintering, crushing, repressing and resintering, the low melting pointconstituent may be introduced into this mixture by means of capillaryaction at temperatures above the melting point of the low temperatureconstituent. Repressing and resintering, with or without furtheroperations, may also be applied in this case. In certain instances ithas been found advisable to combine the above mentioned manufacturingprocedures by substituting various steps of the one procedure withcertain steps of the second procedure.

There are also certain possibilities of varying It may, for instance,

be desirable to spray the low melting point constituent onto the pressedbody of the sintered refractory material, and then heat same to absorbthe sprayed-on layer of the low melting point material. Instead ofspraying, other processes such as plating, may also be used.

By means of these methods, excellent metal compositions are obtained,the structure of which is homogeneous and the bodies of which may beeasily prepared. Such bodies will also retain, over long periods oftime, their original homogeneous structure.

Instead of using a pure nitride of the metal of the fourth or fifthgroup of the periodic system, I have found that I can use commercialgrades of these materials which usually contain a certain percentage ofimpurities. As a matter of fact, in many cases, I have found it verydesirable to have impurities present because they seem to improve thewetting characteristics and form a stronger union between the lowmelting point phases and the refractory metal compounds. Instead ofusing pure nitrides, therefore, I may use also, nitrides contaminatedwith a small percentage of carbon. Such nitrides are generally known ascyano nitrides.

Since certain changes in carrying out the above processes, and certainmodifications in the composition, which embody the invention, may bemade, without departing from its scope, it is intended that all mattercontained in the above description, shall be interpreted as illustrativeand not in a limiting sense. It is also to be understood that thefollowing claim is intended to cover all of the generic and specificfeatures of the invention herein described, and all statements of thescope of the invention, which as a matter of language might be said tofall therebetween.

What is claimed is:

An electric contacting element formed of a metal composition consistingof 50 to 99% of at least one of the nitrides selected from the groupconsisting of nitridesof titanium, zirconium, hafnium, vanadium,columbium and tantalum, and l to 50% of lower melting point metalselected from the group consisting of silver, copper and gold and alloysconsisting'predominantly of said metal.

FRANZ R. HENSEL.

